For retracting gingiva from a prepared tooth a cord can be used. In this respect, a retraction cord is packed between gingival tissue and the margin of the prepared tooth (this region is also often called sulcus) using an appropriate dental instrument. To obtain sufficient vertical and horizontal retraction of gingival tissue, it is often necessary to pack several lengths of retraction cord into the sulcus in order to be able to make a detailed dental impression.
A description of the background in regard to retraction cords can be found e.g. in U.S. Pat. No. 4,522,593.
Generally, dental retraction cords are sometimes difficult to place into the gingival sulcus. The procedure can also be time consuming. Moreover, it can be cumbersome to remove the retraction cord prior to taking the impression. Coagulated blood may adhere to the cord and removing it may open the wound again which may result in bleeding.
For a more convenient placement retraction pastes have been suggested.
Non-hardening retraction pastes containing either an anti-evaporating component or fibrillated fibres are described in e.g. US 2005/000853 and US 2005/028749.
U.S. Pat. No. 5,362,495 refers to a method for widening the gingival sulcus comprising inserting within the gingival sulcus a material in the form of a biocompatible paste which is injectable for external use and having a plastic viscosity measured at 20° C. between about 13,000 and 30,000 Pa*s, wherein said material consisting of a material selected from the group of white clay, seaweed meal and mixtures thereof.
US 2005/0069838 discloses a dental kit and method for retraction sulcus using an expanding silicone compound or mixture of different silicone compounds. However, silicone compounds are of inorganic and hydrophobic nature, thus having limited biocompatibility with oral tissue and disadvantages in flowing to moist tissue and tooth surfaces and moist areas like the gingival sulcus.
In DE 2 142 756 a process for producing a retraction ring is described. A dry powder mixture of blood coagulant, local anaestetic and disinfectant is filled in cavities of a ring by applying gas pressure in a sealed chamber under partial vacuum or by applying the powder mixture under ambient conditions to the surface of the ring.
None of the above outlined procedure is fully satisfying to the practitioner.
Thus, there is still room for improvement especially with regard to the requirements to be fulfilled with respect to modern dental materials.
Ideally, a material is desired, that can easily be inserted into the sulcus and around a prepared tooth.